You freakishly efficient devs must be using assembly or programming in binary!

Thanks for the game :3

Thank you. :)

No assembly programming here - all just high level C#.
What saves so much memory is that I don't really use any textures (aside from font atlas and the logos that play when game starts), mostly short (less than a second long) sound effects and entirely realtime lighting (so no need to store large lightmaps in levels).
Yet, of all the game's size, the music makes up almost half of that (all songs come with variations that allow regular and looping playback).

Excellent!